Gasoline-powered vehicles are widely used for transportation and become indispensible to our daily lives. With rapid development of the related technologies, mass production of gasoline-powered vehicles brings convenience to the human beings. The total number of gasoline-powered vehicles in the world is about 850 millions at present. In addition, 57% of the world's oil consumption (or 67% of the United State's oil consumption) lies in the transportation sector. It is estimated that the total number of gasoline-powered vehicles in the world is about 1.2 billion in 2020. Since there is a net gap between the global oil demand and the oil supply, the unbalance between supply and demand of petroleum energy has become increasingly prominent. It is estimated that the net gap between the global oil demand and the oil supply is nearly twice the world's oil production quantity. Consequently, the oil price is rapidly increased, and the operating cost of the vehicle becomes higher and higher. Nowadays, many countries are actively encouraging the development of new energy vehicles in order to reduce the dependence on oil.
Furthermore, during operations of the gasoline-powered vehicles, the burning of the gasoline may cause air pollution problem and serious environmental problem. For protecting the environment, the manufacturers of vehicles are devoted to the development and research of low pollution vehicles. Among various kinds of new energy vehicles, electric vehicles (EV) are more advantageous because of the well-established technologies. In addition, since the power net is widespread over the world, it is convenient to acquire the stable electric energy. As a consequence, electric vehicles (EV) and hybrid electric vehicles (PHEV) are more important in the development of new energy vehicles.
As known, an electric vehicle or a hybrid electric vehicle has a built-in chargeable battery as a stable energy source. Moreover, a charging station and a charging circuit of the electric vehicle are collaboratively defined as a charging system. The charging system is used for charging the chargeable battery in order to provide electric energy required to power the electric vehicle. Generally, the charging station has an internal power-supplying circuit for receiving an AC input voltage and regulating the voltage level, thereby issuing an AC output voltage to the charging circuit. Nowadays, for generating high output power and achieving power-saving efficacy, the AC input voltage usually has a medium-high voltage level (e.g. 1.2 KV˜22 KV). In addition, the charging station has an isolated transformer. By the isolated transformer, the AC input voltage is reduced to the AC output voltage of 200V˜480V.
FIG. 1 schematically illustrates the architecture of a conventional charging system. As shown in FIG. 1, the conventional charging system 1 comprises an isolation unit 10 and a converting unit 11. The isolation unit 10 comprises a three-phase transformer Tr. Moreover, the isolation unit 10 is included in a charging station (not shown). The three-phase transformer Tr is used for receiving a three-phase AC input voltage Vin (e.g. a medium-high voltage level in the range between 1.2 KV and 22 KV) from a power-supplying terminal (e.g. a utility power source), and reducing and converting the three-phase AC input voltage Vin into a three-phase AC output voltage Vout (e.g. 200V˜480V). The converting unit 11 may be included in the charging station. For example, the converting unit 11 has a two-stage circuitry configuration. The converting unit 11 comprises a three-phase power factor correction circuit 110 (i.e. a first-stage circuit) and a DC-DC converting circuit 111 (i.e. a second-stage circuit). The three-phase power factor correction circuit 110 is electrically connected with the isolation unit 10 for filtering off the harmonic wave component contained in the received current, thereby increasing the power factor. Consequently, the three-phase power factor correction circuit 110 outputs a DC transition voltage Vs. The DC-DC converting circuit 111 is used for converting the DC transition voltage Vs into a DC charging voltage Vc for charging the chargeable battery in the electric vehicle in the range between 50V and 750V.
FIG. 2 schematically illustrates the architecture of another conventional charging system. Component parts and elements of FIG. 2 corresponding to those of FIG. 1 are designated by identical numeral references, and detailed description thereof is omitted. In comparison with FIG. 1, the first-stage circuit of the converting unit 21 of FIG. 2 comprises three sets of single-phase power factor correction circuits 210. Corresponding to the first-stage circuit, the second-stage circuit of the converting unit 21 of FIG. 2 comprises three sets of DC-DC converting circuits 211. Each single-phase power factor correction circuit 210 is electrically connected to two different phases of the output side of the isolated transformer Tr. Moreover, the three sets of DC-DC converting circuits 211 are electrically connected with corresponding single-phase power factor correction circuits 210, respectively. Moreover, the output terminals of these DC-DC converting circuits 211 are connected with each other in parallel. In such way, the three-phase balance of the input current is achieved, and the chargeable battery is charged by the DC charging voltage Vc.
Please refer to FIGS. 1 and 2 again. Since the three-phase transformer Tr is only configured to provide an isolating function but unable to filter off the harmonic wave, the three-phase power factor correction circuit 110 of the charging system 1 and the single-phase power factor correction circuits 210 of the charging system 2 are necessary to filter off the harmonic wave, thereby increasing the power factor. Since the circuitry configuration of the three-phase power factor correction circuit 110 or the single-phase power factor correction circuit 210 is very complicated and the number of the electronic components thereof is very large, the charging system 1 or 2 is high. Moreover, since the conventional charging system 1 or 2 has the two-stage circuitry configuration, the real working efficiency is influenced by the conversion loss of the DC-DC converting circuit 111 or 211 and the conversion loss of the three-phase power factor correction circuit 110 or the single-phase power factor correction circuit 210. Consequently, if the three-phase AC input voltage Vin is in the range between 1.2 KV and 22 KV, the conversion efficiency of the conventional charging system 1 or 2 may reach only 89%˜93%.
In FIGS. 1 and 2, the conventional charging system 1 or 2 is applied to the electric vehicle. Nevertheless, the conventional charging system 1 or 2 may be applied to other fields. For example, the conventional charging system 1 or 2 may be applied to an internet data center with at least one sever in order to charge a chargeable battery of server. However, the conventional charging system 1 or 2 applied to the internet data center also has the above problems.
Therefore, there is a need of providing an improved charging system in order to reduce the fabricating cost and enhancing the conversion efficiency.